Foot-guided nailing machine



United States Patent 3,107,355 FOOT-GUIDED NAILING MACHINE Allan C.Swanson, Snnland, Calif., assignor, by mesne assignments, to Nu-MatieNailer International Corp, Los Angeles, Calif., 'a corporation ofCalifornia Filed Oct. 26, 1960, Ser. No. 65,048 6 Claims. (Cl. 1-106)This invention relates to foot-guided nailing machines, moreparticularly to nailing machines of the type disclosed in Patent No.2,546,354 issued March 27, 1951, to C. J. Bacon et al., entitled,Nailing Machine. Nailing machines of this type are primarily adapted fornailing subrooiing and subfiooring to rafters and floor joists.

Included in the objects of this invention are:

First, to provide a nailing machine utilizing a power hammer having anail-driving pin, and which incorporates novel automatic control meanswhereby the nailing operation automatically commences when the operatorsets the machine with a nail in the barrel against a board and moves thenail-driving pin into operative engagement with the nail, andautomatically stops when the nail is driven flush or is countersunk apreselected'distance so that the quality of the nailing operation is notdependent upon the skill of the operator.

Second, to provide a nailing machine which is so arranged that the powerhammer is not activated unless movement of the nail-driving pin isinitially arrested by a nail in the barrel of the machine, and with itspoint bearing against a board or other member underlying the barrel, sothat unless a nail is in the barrel and the barrel is held against anunderlying surface the nailing operation cannot occur.

Third, to provide a nailing machine having a power hammer whichincorporates a novel valve and control means so arranged that themachine may accommodate different lengths of nails without adjustment ofthe control means, as the power hammer is not activated until the nailis engaged, irrespective of its length, but which may be readilyadjusted to ensure that all nails are driven precisely to the desireddepth.

Fourth, to provide a nailing machine which incor porates magnetic meansassociated with the nail-guiding bore to prevent the nail from droppingfrom the machine as it is moved from one nailing location to another.

With the above and other objects in view, as may appear hereinafter,reference is directed to the accompanying drawings in which:

FIGURE 1 is a side view of a nailing machine with the parts shown in thepositions assumed at the start of the nail-driving cycle;

FIGURE 2 is a longitudinal, partial elevational, partial sectional viewtaken through 22 of FIGURE 1 with the handle shown fragmentarily;

FIGURE 3 is a fragmentary, partial sectional, partial elevational viewtaken through 3-3 of FIGURE 2, that is, in a plane parallel with FIGURE1;

FIGURE 4 is an enlarged, transverse, sectional View taken through 4-4 ofFIGURE 1, showing particularly the inlet passages to the valvemechanism;

FIGURE 5 is an enlarged, fragmentary, sectional view taken through '55of FIGURE 4 showing the valve mechanism;

FIGURE 6 is a fragmentary, partial sectional, partial side view takenthrough 6-6 of FIGURE 4 showing another portion of the valve mechanism;

FIGURE 7 is an enlarged, transverse, sectional view taken through 7-? of'FIGURE' 2, illustrating the relationship of the valve-operating fingerWith the operating end of the pneumatic hammer assembly;

FIGURES 8, 9, l0, and 11 are substantially diagrammatical views with theparts rearranged to bring them into a common plane, in order toillustrate the operation of the nailing machine. More particularly,FIGURE 8 shows the relationship of the parts of a machine at thecommencement of the nailing cycle before engagement of the nail by thenail-driving pin; FIGURE 9 illustrates a subsequent position in whichthe nail-driving pin has moved into engagement with the nail; FIGURE 10shows a subsequent position of the machine when the nail has been drivento its final position; and FIGURE 11 shows the position of the parts asthe nail-driving pin is being retracted just before movement to theinitial position shown in FIGURE 8.

The foot-guided nailing machine utilizes a pneumatic hammer assemblywhich may be in most respects conventional. The hammer assembly includesa handle 1 which in the conventional hammer assembly may also serve asthe means for conducting air to the hammer. In the exercise of thepresent invention, the air is supplied through the side of the pneumatichammer assembly, as will be described hereinafter, and the passagethrough the handle is closed off.

Below the handle 1 the hammer assembly includes a tubular stem 2 whichis joined to a conventional cylinder structure 3 from which protrudes areciprocable plunger 4. In the exercise of the present invention, thecylinder structure is modified by the addition of a sleeve 5 whichencloses the upper portion of the plunger 4 and also encloses aconventional retainer spring 6. The plunger 4 is modified to form aflange 7. The lower end of the sleeve 5 and the upper side of the flange'7 serve to operate a control means for a valve structure which will bedescribed hereinafter.

Fitted in the lower end of the plunger 2- is a nail-driving pin 8. Thelower end of the pneumatic hammer assembly, that is, the lower end ofthe cylinder structure 3 and sleeve 5 are adapted to enter a cylindricalbarrel 9. The lower end of the barrel 9 is reduced in diameterinternally to receive a cylindrical nosepiece 10. The nosepiece l0protrudes slightly from the lower end of the barrel 9 and is providedwith an external flange 11 to limit upward movement of the nosepiecewithin the barrel 9.

The nosepiece 10 is provided with a central bore 12 adapted to receivenails N, and also to receive the naildriving pin 8 so that nails may bedriven downwardly through the bore 12 into an underlying board.

At least one side of the nosepiece 10 is provided with a groove 13 whichreceives the lower inturned end of an L-shaped retainer bar 14. Theretainer bar includes an upright portion extending vertically through aguide member 15 secured to the side of the barrel 9. The verticalportion of the retainer bar 14 receives a spring 16 and an adjustablecollar 17. The retainer bar yieldably retains the nosepiece 10 withinthe barrel 9.

At approximately right angles to the groove 13, the nosepiece 10 isprovided in its side Wall with a riail-receiving slot 18 which registerswith a nail-receiving slot 19 formed in the barrel 9. Extending upwardlyfrom the slotted side of the barrel 9 is a bracket 20 which pivotallymounts a nail hopper 21. The bracket 20' also incorporates anail-feeding mechanism 22 so that nails may be dropped, one at a time,downwardly alongside the barrel 9. The nails when dropped are deflectedby a pi-votally mounted guide finger 23 into the slots 19 and 18 fordelivery to the bore 12 of the nosepiece 10. The nail hopper 21 includesa hopper arm 24 which extends across and at one side of the axis of thebarrel 9, and is connected by a link 25 to a clamp 26 secured to theupper portion of the cylinder structure 3.

Except for minor changes in the construction of the pneumatic hammerassembly to facilitate cooperation with the valve structure forming apart of the present invention, the previously described structure may beconsidered as conventional and is in fact more completely disclosed inthe previously mentioned Patent 2,546,354. More particularly, thebackground structure for cooperation with the present invention involvesthe barrel 9 and nosepiece 10 with means for feeding nails, one at atime, so as to be received in the bore 12 for engagement by thenail-driving pin 8 and the associated pneumatic harnmer assembly whichis adapted to be manually reciprocated relative to the barrel 9 so as tomaintain the naildriving pin 8 in engagement with the nail during thedriving operaton and to raise the nail-driving pin so that a succeedingnail may be received in the bore 12. In the exercise of the presentinvention, a novel valve mechanism is provided which is designed tosupply air to the pneumatic hammer, as the nail-driving pin 8 is broughtmanually into position for engagement with a nail, and automaticallyterminates the supply of air to the hammer when the nail has beendriven, either flush with an underlying board or has been countersunk apredetermined distance therein.

The valve mechanism includes a valve body 27 which is provided with asemicylindrical side 28 held against the tubular stem 2 by a matingsemicylindrical clamp member 29. The upper side of the valve body 27 isprovided with an inlet passage 39 which communicates with the side of aprimary valve bore 31 disposed vertically in the valve body 27. Theupper end of the primary valve bore 31 is provided with a shoulder whichforms a valve seat 32 controlling the flow through a connecting passage33, which leads to the upper end of a secondary valve bore 34 alsodisposed vertically in the valve body 27. The secondary valve bore 34 isprovided intermediate its ends with a liner 35 having a socket 36therein, the upper end of which forms a valve seat. The liner 35 isprovided with a side port which communicates through a passage 37 to theinterior of the tubular stem 2. The passage 37 may include a verticalchannel defined by confronting walls of the cylindrical side 28 of thevalve body 27 and the tubular stem 2, as shown best in FIGURE 5.

The primary valve bore 31 is provided with a primary valve 38 whichengages the valve seat 32. The primary valve is provided with adownwardly extending valve stem 39 which extends downwardly through aguide liner 48 having suitable sealing elements. The lower portion ofthe valve stem 39 below the guide liner 40 is provided with an extendedscrew-threaded portion on which is screw-threaded an adjustable sleeve41. The lower end of the valve stem 39 protrudes from the sleeve 41 andis screw-threaded into a lock collar 42, which in turn is screw-threadedonto the upper end of a connecting rod 43 and secured thereto by a locknut 44. The adjustment sleeve 41 is provided with a pair of spaceddetent grooves 45, either one of which is engageable by a ball detent 46so as to retain the primary valve 38 either in an open position, asindicated in FIGURE 6, or in its closed position.

The connecting rod 43 is provided with an extended screw-threadedportion which receives an adjustable stop nut 45. The lower end of theconnecting rod 43 terminates in an end flange 46. Above the end flange46 the connecting rod 43 receives a lower and upper cushion spring 47and 48. Secured to the side of the barrel 9, opposite from the retainerbar 14, by means of screws 49, is a strap 50 which extends upwardly andforms an offset portion 51 terminating at its upper end in a horizontalbracket 52. The bracket 52 guides the lower end of the connecting rod 43and is interposed between the cushion springs 47 and 48. As will bebrought out hereinafter, manual relative movement of the pneumatichammer assembly and the barrel 9 effects movement of the primary valve38 between its open and closed positions.

The secondary valve bore 34 receives a secondary valve 53 adapted toengage the valve seat formed at the upper end of the liner socket 36. Aspring 54 disposed above the secondary valve 53 tends to hold the valveon its seat. The liner 35 is fixed in position by a screw indicated bydotted lines in FIGURE 5. The secondary valve 53 is provided with a stem55 which extends downwardly through the liner 35. Freely slidable in thesecondary valve bore 34 below the liner 35 is a shuttle plunger 56 whichis urged downwardly by the stem 55.

The valve body 27 is provided below the secondary valve bore 34 with apilot valve bore 57, preferably extending horizontally into the valvebody from one side thereof. Slidably mounted in the pilot valve bore 57is a pilot valve 58, the outer end of which is adapted to protrude fromthe bore 57 and the valve is urged outwardly by a spring 59. The pilotvalve 58 is provided with an annular groove 60 isolated from the pilotvalve bore 57 by suitable seal rings. An air supply passage 61 extendsfrom the upper part of the secondary valve bore 34 above the liner 35 tothe side of the pilot valve bore 57 for communication with the annulargroove 60. A connecting passage 62 axially offset from the air supplypassage 61, with respect to the pilot bore 57, communicates between thepilot valve bore and the lower end of the secondary valve bore 34. Atthe extreme inner end of the pilot valve bore 57 there is provided anexhaust or vent passage 63 extending to the outside of the valve body27. The relationship of the passages 61, 62, and 63 with respect to thepilot valve bore 57 and pilot valve 58 is such that the pilot valve 58may occupy an outer or extended position such as shown in FIGURE 5,whereby the connecting passage 62 and exhaust passage 63 affordcommunication with the lower end of the secondary valve bore 34; andoccupy an axially inner position in which the air supply passage 61 andthe connecting passage 62 are in communication. Immediately below theliner 35, the secondary valve bore 34 is also provided with an exhaustpassage 64.

The valve body 27 is provided with a vertical slot 65 which intersectsthe outer end of the pilot valve bore 57. Pivotally mounted in the slot65 is a latch lever 66, a pivot pin 67 being provided at a level abovethe pilot valve bore 57 so that the latch lever 66 depends therefrom andextends below the valve body 27.

The clamp 26, which is connected by the link 25 to the hopper arm 24,may also include a bracket arm 68, which secures a vertically disposedguide tube 69. The upper end of the guide tube 69 is cut away on oneside and its remaining side overlies the slot 65 so as to cover thelatch lever 66. An operating rod 70 is slidably mounted in the guidetube 69. The upper end of the operating rod 70 is beveled and providedwith a latch notch Z1 which cooperates with the beveled lower end of thelatch lever 66 and a notch 72 adjacent thereto.

The operating rod 70 is provided with a laterally extending finger 73adapted to extend through a slot 74 formed in the barrel 9. The tip endof the finger 73 terminates in an :arcuate portion 75 adapted to fit inthe annular groove or channel formed between the sleeve 5 and the flange7.

In order to prevent loss of nails from the bore 12 of the nosepiece 10,the nosepiece and adjacent wall of the barrel 9 are slotted to receive amagnet 76, which may be retained in place by the lower end of the strap50. To facilitate use of the magnet 76, the nosepiece 10 and barrel 9are formed of nonmagnetic material.

The lower end of the barrel 9 forms a spherical zone and is adapted toreceive a correspondingly-shaped collar 77 for limited universalmovement. Extending laterally of the collar 77 is a stirrup 78 adaptedto receive a persons foot. The stirrup 78 is a conventional part of thenailing machine, and is also shown in Patent No. 2,546,354.

Operation of the foot-guided nailing machine is as follows:

The nailing machine is lifted slightly and moved from place to place bythe operators foot. The operator also raises and lowers the handle 1 tomove the pneumatic hammer assembly relative to the barrel 9, and at thesame time to actuate the nail hopper 21 and nail-feeding mechanism 22 sothat nails may be delivered, one at a time, with each raising andlowering of the handle 1 to the slots 19 and .18, so as to be received,one, at a time, in the bore 12 of the nosepiece In this respect theoperation of the machine is essentially the same as that shown in theabove-mentioned patent.

The herein described valve mechanism which controls the supply of air tothe pneumatic hammer is best illustrated in the diagrammatical views inFIGURES 8, 9, 10, and 11. In this regard, it should be noted that thevalve body 27 is fixed to the pneumatic hammer assembly and movestherewith.

With reference first to FIGURE 8, when a nail has been received in thebore .12 of the nosepiece 10 and the pneumatic hammer assembly includingthe valve body 27 has been raised to its upper extreme position, thebracket 52 of the strap 50 has engaged the lower cushion spring 47 so asto draw the primary valve 3% downward to permit the flow of air from theinlet passage 30 to the secondary bore 34. In this condition of thevalve structure, the secondary valve 53 is held against the valve seatat the upper end of the socket 36 and the liner -35; the shuttle plunger56 is in its lower position; the pilot valve 58 is in its outer positionso that both sides of the shuttle plunger 56 are exposed to atmosphericpressure. With this arrangement of the parts, air does not flow to thepneumatic hammer.

Reference is now directed to FIGURE 9. When the pneumatic hammerassembly and valve body are moved downward until movement of thenail-driving pin 8 is arrested by a nail in the bore 12, the flange 7engages the finger 73 so that downward movement of the rod 70 is alsoarrested. This causes the upper end of the rod 70 to engage the latchlever '66 so as to force the pilot valve 58 inward, thereby connectingpassages 61 and 62 to the groove 69 so as to supply air to the undersideof the shuttle plunger 56. Upward movement of the shuttle plunger 56raises the stem 55 and secondary valve 53, so as to raise the valve fromits seat and permit the flow of air to the pneumatic hammer assembly andinitiate the nail-hammering operation.

Reference is now directed to FIGURE 10. Flow of air continues until theadjustable stop nut 45 engages the upper cushion spring 48 so that theprimary valve 38 is moved to its closed position. The level in thedownward movement of the nail-driving pin 8 at which the air supply iscut off may be accurately predetermined by the adjustable stop nut 45.Consequently, the nail may be driven fiush with an underlying board orcountersunk a preselected distance. When the air supply to the primaryvalve 38 is shut off, air supply through the pilot valve to theunderside of the shuttle plunger 56 is also shut off, consequently thespring 54 returns the secondary valve 53 to its seat. The operating rod70 and latch lever 66, however, remain interengaged.

Reference is now directed to FIGURE 11. When the pneumatic hammerassembly and valve structure is raised from the position shown in FIGURE10 toward the position shown in FIGURE 8, the finger 73 connected to theoperating rod 70 engages the upper extremity of the slot 74, so thatcontinued upward movement of the pneumatic hammer assembly and valvestructure raises the latch lever 66 out of engagement with the operatingrod 70. By reason of interengagement between the lower cushion spring 47and the bracket 52, the pilot valve 57 is permitted to move to its outerposition shown in FIG- URE 8. Until the pneumatic hammer assembly andvalve structure are fully raised, the conditions shown in FIGURE 8obtain.

During the nail-driving cycle, that is, during the movement of thenail-driving pin 8 from the position shown 6 in FIGURE 9 to the positionshown in FIGURE 10, and the return movement of the nail-driving pin 8 toits upper position shown in FIGURE 8, a new nail is received in the bore12 of the nosepiece 10 so that the cycle of operations represented IbyFIGURES 8, 9, 10, and 11 may be repeated.

It will be observed that until the downward movement of the nail-drivingpin 9 is arrested by a nail in the bore 12, the pneumatic hammer remainsinactivated. the nail itself must be held'from movement by engagement ofits point with an underlying board or other member. If the barrel israised or if there is no nail in the bore 12, the pneumatic hammerremains inactivated.

It will also be observed that without adjustment various lengths ofnails may be accommodated, as the pneumatic hammer will not begin itsoperation until a nail is engaged by the nail-driving pin 8.

While a particular embodiment of this invention has been shown anddescribed, it is not intended to limit the same to the exact details ofthe construction set forth, and it embraces such changes, modifications,and equivalents of the parts and their formation and arrangement as comewithin the purview of the appended claims.

What is claimed is:

l. A nailing machine, comprising: a pneumatic hammer assembly includinga nail-driving element; a barrel structure defining a bore for receivinga nail and said driving element, and means vfor feeding nails insequence to said bore; means connecting said assembly and structure foroperating said feeding means and manually operable for moving saiddriving element in said bore; a control valve mounted on said pneumatichammer assembly and including first and second series related valveunits for controlling the flow of air to said pneumatic hammer assembly;a first control means engageable with said barrel structure prior toengagement of said driving element with a nail in said barrel structurebore to open said first valve unit, and engageable with said barrelstructure when said nail-driving means has driven a nail a predetermineddistance to close said first valve unit; and a second control meansengageable with said nail-driving element and said barrel structure toopen said second valve unit subsequent to said first valve unit andinitiate operation of said pneumatic hammer assembly as saidnail-driving element engages a nail in said barrel, and to close saidsecond valve unit prior to opening of said first valve unit.

2. In a nailing machine having a pneumatic hammer assembly including anail-driving element, a barrel structure having a nail-receiving bore,and means for feeding nails to said bore, wherein said pneumatic hammerassembly and barrel structure are relatively movable manually to operatesaid nail-feeding means and to bring said nail-driving element intooperative engagement with a nail in said bore, a control means for saidpneumatic hammer, com-prising: a valve body mounted on said pneumatichammer assembly for movement therewith; series-related primary andsecondary valve units in said valve body for controlling flow :of air tosaid pneumatic hammer assembly; primary and secondary control devicesfor said valve units operably connected with said pneumatic hammerassembly and with said barrel structure; said primary control deviceincluding setting means operable to open said primary valve when saidnail-driving element is positioned to permit entry of a nail into thebore of the barrel structure, and adjustable terminating means operableafter said nail-driving element has driven a nail a predetermineddistance to close said primary valve unit; said secondary control deviceincluding means operable subsequent to said setting means to open saidsecondary valve as said nail-driving element engages a nail in saidbore, to initiate operation of said driving means, and to close saidsecondary valve after operation of said terminating means thereby toreset said secondary valve unit for subsequent operation of said settingmeans.

3. In a nailing machine having a pneumatic hammer assembly including anail-driving element, a barrel structure having a nail-receiving bore,and means for feeding nails to said bore, wherein said pneumatic hammerassembly and barrel structure are relatively movable manually -tooperate said nail-feeding means and to bring said nail-driving elementinto operative engagement with a nail in said bore, a control means forsaid pneumatic hammer, comprising: means responsive to relative movement of said pneumatic hammer assembly and barrel structure as saidnail-driving element engages a nail in the bore of said barrel structureto initiate operation of said pneumatic hammer assembly thereby to drivea nail from said bore; and adjustable means to terminate operation ofsaid pneumatic harmner assembly when said nail has been driven apredetermined distance.

4. A control means for a nailing machine having a pneumatic hammerassembly including a nail-driving eiement, a barrel structure having anail-receiving bore, and means for feeding nails in sequence to saidnail-receiving bore, said pneumatic hammer assembly being relativelymovable manually to operate said nail-feeding means, and to move saidnail-driving element into engagement with a nail in said bore, furthermovement of the nail-driving element being arrested when the point ofthe nail rests against a board underlying the barrel structure, saidcontrol means comprising: a valve structure mounted on said pneumatichammer assembly including a series-related primary and secondary valveunit; a primary control operable to open said primary valve unit whensaid pneumatic hammer assembly and barrel structure are relativelypositioned for delivery of a nail to said nail-receiving bore, and toclose said primary valve unit when a nail has subsequently been driven apredetermined distance by said nail-driving means; and a secondarycontrol sensitive to said arresting of said nail-driving means by a nailin said nail-receiving here to open said secondary valve unit thereby toinitiate operation of said pneumatic hammer assembly.

5. A nailing machine, comprising: a pneumatic hammer assembly includinga cylinder structure and a hammer structure having limited movementrelative to said cylinder structure and terminating in a nail-drivingelement; a barrel structure adapted to receive said cylinder structureand hammer structure and having a nail-receiving bore also adapted toreceive said nail-driving element; said pneumatic hammer assembly andbarrel structure adapted to occupy a relatively extended position toreceive a nail in said bore under said nail-driving element, and arelatively retracted position to displace a nail from said bore by saidnail-driving element, movement of said nail-driving element beingarrested when the point of said nail rests on a board underlying saidbarrel structure, thereby to cause relative movement between thenail-driving element and the cylinder structure of said pneumatic hammerstructure; and a valve structure for controlling said pneumatic hammerassembly including means sensitive to said relative movement of saidnail-driving element and said cylinder structure when movement of saidelement is arrested by a nail in said nail-receiving bore to initiateoperation of said pneumatic hammer assembly and said nail-drivingelement, and means operable to terminate operative of said pneumatichammer assembly when said nail has been driven a predetermined distance.

6. A nailing machine, comprising: a pneumatic hammer assembly includinga cylinder structure and a hammer structure having limited movementrelative to said cylinder structure and terminating in a nail-drivingelement; a barrel structure adapted to receive said cylinder structureand hammer structure and having a nail-receiving bore also adapted toreceive said nail-driving element; said pneumatic hammer assembly andbarrel structure adapted to occupy a relatively extended position toreceive a nail in said bore under said nail-driving element, and arelatively retracted position to displace a nail from said bore by saidnail-driving element, movement of said nail-driving element beingarrested when the point of said nail rests on a board underlying saidbarrel structure, thereby to cause relative movement between thenail-driving element and the cylinder structure of said pneumatic hammerstructure; a valve body mounted on said pneumatic hammer assemblyincluding a first valve unit and a second valve unit disposed in series;setting means for opening said first valve unit when said pneumatichammer assembly and barrel structure are relatively extended; initiatingmeans sensitive to arresting of said nail-driving element by a nail inthe bore of said barrel structure to open said second valve thereby toinitiate operation of said pneumatic hammer assembly; and adjustableterminating means connected with said setting means for terminatingoperation of said pneumatic hammer assembly when said nail has beendriven a predetermined distance.

References Cited in the file of this patent UNITED STATES PATENTS2,799,858 Bacon July 23, 1957

1. A NAILING MACHINE, COMPRISING: A PNUEMATIC HAMMER ASSEMBLY INCLUDINGA NAIL-DRIVING ELEMENT; A BARREL STRUCTURE DEFINING A BORE FOR RECEIVINGA NAIL AND SAID DRIVING ELEMENT, AND MEANS FOR FEEDING NAILS IN SEQUENCETO SAID BORE; MEANS CONNECTING SAID ASSEMBLY AND STRUCTURE FOR OPERATINGSAID FEEDING MEANS MANUALLY OPERABLE FOR MOVING SAID DRIVING ELEMENT INSAID BORE; A CONTROL VALVE MOUNTED ON SAID PNEUMATIC HAMMER ASSEMBLY ANDINCLUDING FIRST AND SECOND SERIES RELATED VALVE UNITS FOR CONTROLLINGTHE FLOW OF AIR TO SAID PNEUMATIC HAMMER ASSEMBLY; A FIRST CONTROL MEANSENGAGEABLE WITH SAID BARREL STRUCTURE PRIOR TO ENGAGEMENT OF SAIDDRIVING ELEMENT WITH A NAIL IN SAID BARREL STRUCTURE BORE TO OPEN SAIDFIRST VALVE UNIT, AND ENGAGEABLE WITH SAID BARREL STRUCTURE WHEN SAIDNAIL-DRIVING MEANS HAS DRIVEN A NAIL A PREDETERMINED DISTANCE TO CLOSESAID FIRST VALVE UNIT; AND A SECOND CONTROL MEANS ENGAGEABLE WITH SAIDNAIL-DRIVING ELEMENT AND SAID BARREL STRUCTURE TO OPEN SAID SECOND VALVEUNIT SUBSEQUENT TO SAID FIRST VALVE UNIT AND INITIATE OPERATION OF SAIDPNEUMATIC HAMMER ASSEMBLY AS SAID NAIL-DRIVING ELEMENT ENGAGES A NAIL INSAID BARREL, AND TO CLOSE SAID SECOND VALVE UNIT PRIOR TO OPENING OFSAID FIRST VALVE UNIT.